Carbon black



5 Jan. 15, 1935. E. B. SPEAR ET AL 1,987,644

' CARBON BLACK Filed Feb. 4, 1935 2 Sheets-Sheet 1 INVENTORS ELwovdBSp'earfiRohertLMm 5 km 144.. c

ATTR/VEY Jan. 15, 1 935. E. B. SPEAR ET AL CARBON BLACK Filed Feb. 4. 1933 2 Sheets-She et 2 A '1 my INVENTORS ElwwdBJ neqr 6 Robert LMM By J Patented Jam-r5, 1935 UNITED STATES CARBON BLACK Ellwood B. Spear, Milford, N. H., and Robert L. Moore, Mount Lebanon, Pa., assignorsto Ther matomic Carbon Company, New York, N. corporation of Delaware Application February 4, 1933, Serial No. 655,296 In Canada August 18, 1928 11 Claims.

This application is .a continuation in part of our co-pending application Serial'No. 484,578, filed September 26, ,1930, which is a divisiorr of our co-pending Serial No. 300,132, filed August 16, 1928, as a continuation in part of our co-pending application Serial No. 61,149, filed October 7, 1925 now U. S. Patent No. 1,911,003, granted May 23, 1933, and Serial No. 206,500, filed July 18, 1927-, now abandoned, and which related to the carbon of the present application and the method of producing same which comprised passing the mixture of hydrocarbon and inert diluent gases through highly heated refractory checkerwork.

The present invention relates to carbon black. This carbon black is a variation and an improvementv in carbon blacks of the so-called thermal decomposition type. i The thermal decomposition carbons differ from the common commercial car-'- bon blacks in having markedly less rubber-stiffening qualities. blacks are ordinarily made by gas flames burning against cool metal surfaces upon which the car-' bon black is deposited and from which it is scraped. This process is commonly called the channel process, and these blacks are sometimes called channel blacks. blacks of the thermal decomposition type are usually made by decomposing the gas in a heated retort. as described for example, in the Brownlee and Uhlinger Patent No. 1,520,115 of December 23, 1924, or by variations of such process, such for example, as the process hereinafter described. The term thermal decomposition therefore apv.plies to a plurality of carbon blacks and is the name of a type. One particular variety of thermal'decomposition carbon black is that manufactured according to the process of the Brownlee and Uhlinger patent referred to above, and is known to the trade under its particular registered blac trade-mark. The thermal decomposition carbon black as made by the process hereinafter described is likewise known to the trade by its registered trade-mark, but it will be referred to herein merely as "our carbon black" or-our new carbon Au ust 9, 1927. .These' characteristics, an'dfparticularly the rubber-stiffening qualities, difler somewhat from those described in the Brownlee The common commercial carbon The carbon and Uhlinger Patent No. 1,478,730,. datedDecember 25, 1923, as it has been found that the carbon black, as made commercially by the Brownlee and Uhlinger process, has a substantial stifiening efiect upon rubber, although such stiffening eifect is much less than that of common commercial carbon black and approximates the stiffening qualities of zinc oxide.

In said Uhlinger Patent No. 1,638,421, the characteristics of common commercial carbon black and the thermal decomposition carbon as made by the Brownlee and Uhlinger process are stated in detail and compared, and need not be here repeated.

common commercial carbonblacks and the Brownlee and Uhlinger carbon black. It has cer-' tain of the desirable qualities of both of these carbon blacksand certain additional qualities. Generally speaking, our new carbon black has the low rubber stiffening qualities of the Brownlee and Uhlinger carbon black and the apparent gravity of the common commercial carbon blacks, such as are made by the channel process. It imparts an ultimate tensile strength to rubber approximately equal to that imparted by an equal weight of the best grades of common commercial carbon black. By ultimate tensile strength is meant the tensile strength at point of rupture. It is usually calculated in pounds per square inch on the original cross section of the test piece. It imparts to the rubber a greater elongation at the point of rupture than that imparted by equalweights of either common commercial carbon black or the Brownlee and Uhlinger carbon black. A somewhat greater proportion by weight of our new carbon black may be milled into rubber and the desirable qualities of .the rubber composition retained, than is the case with the Brownlee and. Uhlinger carbon black.

v The rubber composition in which our new car: bon black is compounded therefore differs from rubbercompositions as heretofore made, either with common commercial carbon blacks, or with the Brownlee and Uhlinger carbon black. Our

new carbon black itself, as above described, has certain desirable characteristics which make-it an improvement over the Brownlee and Uhlinger carbon black for certain purposes. These different characteristicsare imparted to the black by its process of manufacture, as hereinafter described. Our preferred process resembles the Brownlee and Uhlinger processin that the .hy-

-drocarbon gas is decomposed-in a retort without substantial combustion of the gas, Our process differs, however, from the Brownlee and Uhlinger process in that the hydrocarbon-gas is mixed with a diluent gas.

Claims directed to the compounding of our new carbon black with rubber stocks and the rubber compositions produced thereby are presented in our U. S. Patent No. 1,794,558, granted March 3,

We will now describe in detail the manufacture of our carbon black and its characteristics.

In the drawings:

Figure 1 is an elevation taken partly in vertical section showing more or less diagrammatically the preferred apparatusfor carrying out the process; and

Figure 2 is a vertical section through the center of the heating retort in the plane parallel to that shown in Figure 1.

The preferred apparatus as shown is that of the general type shown in the Brownlee and Uhlinger Patent No. 1,520,115. Generally speaking, it consists of a heating retort which contains refractory checkerwork. This checkerwork is heated to a high temperature by a heating blast. The heating blast is periodically cut off and the hydrocarbon gas to be decomposed, usually natural gas, is passed through the heated checkerwork and is decomposed thereby into hydrogen and solid carbon particles. Part of the carbon particles are deposited on the checkerwork but part of them are swept alongwith the gas, which passes out through devices for cooling it and filtering out and recovering the entrained carbon.

a spray 4' is discharged to cool the gas. The gas is highly heated and converts the water into steam, the latent heat of evaporation serving efficiently to cool the gas. The gas then passes downwardly through a column 5 and along a conveyor passage 6 into the separating chamber 7, where the gas passes through fabric bags 8, which are shaken from time to time to dislodge the carbon. The carbon from the separator 7 and the tower 5 falls into the conveyor passage 6 where it is pushed along to the right, as viewed.

in Figure 1, by means of the screw conveyor 9 to a bin, from which it is bagged. The. general layout as above described, and particularly the means for coolingthe gas and collecting the carbon black, is described in the Brownlee and Uhlinger Patent No. 1,520,115. The temperature of the cooling chamber 3 is preferably automatically thermostatically controlled, as described in the Brownlee and Uhlinger patent.

The gas from which the entrained carbon particles have been removed goes from the separator 7 into a discharge pipe 10, having two branches 11 and 12. The branch 11 leads back to the retort 1 through a gas storage tank 11a (shown diagrammatically and greatly reduced size) and permits the hydrogen'gas formed to be recirculated through the retort asthe diluent gas,

if desired.

The branch 12 leads off the excess hydrogen which may be.utilized for any desired purpose, such as in the manufacture of ammonia, ferti- 1izer, etc., or even for fuel. A blower 13 is prothe hydrogen gas into the re- The retort 1 has a steel plate casing 14 and a lining consisting of an inner facing 15a of firebrick and a layer 15b of insulation of refractory insulating material, such as asbestos or the porous insulating materials formed from diatomaceous earth such as a well-known trade-marked material which analyzes on ignited bases approximately 93.6% $102, 3.7% A1203, 1.3% FeaOa, 0.7% CaO, 0.6% M80. The chamber within the retort is filled, for the most part, with checkerwork 16 made of refractory brick, usually silica brick. The checkerwork is divided into two parts or zones; first, the zone A in which the diluent gas is preheated; and second, the zone B or reaction zone in which the hydrocarbon gas is decomposed.

The checkerwork in the retort is periodically Y heated by a heating blast admitted through the pipe 17, at the base of the retort. A combustible gas, such for example, as natural gas, is admitted by the branch pipe 18, and air is admitted by the branch pipe 19, to the blast pipe 17 and into the space 20 at the bottom of the retort, where the gas burns and the hot products of combustion pass up through the checkerwork to heat it. During the heating blast, the products of combustion are discharged through the opening-21,

having a closure valve 22, which is lifted during the heating blast, but which is. closed to exclude air' from the retort when the hydrocarbon as is being decomposed. The products of combustion from the heating blast are discharged into a hood 23, and through a stack 23a through the roof of the building.

After the checkerwork 16 has been heated, the A gen gas is admitted to the inlet pipes 24 through thevalves 25 from the gas tank 11a.

- The diluent gas passes into the open diffusing chamber 30 in the top of the retort and down through the checkerwork zone A to the mixing chamber 31, where it meets the hydrocarbon gas to be decomposed which is introduced through the pipes 32. The hydrocarbon gas to be decomposed is usually referred to as the run gas in this industry. There are preferably a plurality of the gas admission pipes 32 so as to insure a thorough mixing in the chamber 31 of the hydrocarbon gas andthe diluent gas. The mixed hydrocarbon gas and diluent gas then passes down through the checkerwork reaction zone B, in which the hydrocarbon gas is decomposed into hydrogen and solid particles. Part of the carbon is deposited upon the checkerwork brick, but part'of it is swept along'through the retort is being heated by the heating blast from the burner pipe 1'7. As shown in the drawings,

- the checkerwork of the zone A is spaced from the Y the diluent "gas is preferably in excess of that of checkerwork of the zone B bysupporting colunms 38, so as to form a relatively unobstructed chamber 31 in which the hydrocarbon gas discharged inwardly from the plurality of inlets 32 may be quickly and thoroughly mixed with the downwardly flowing current of diluent gas. The inlets 32 are fitted with hydrocarbon supply pipes 33 and their valves 35, and with branch pipes 34 and their corresponding valves 36. The latter merely serve for the introduction of auxiliary reactants or diluents if desired. The checkerwork of zone B is likewise supported on columns 39,

Branch pipes 26, controlled by valves 28 areshown at the. top of the retort. This branch pipe is not normally used, but may be used in a modification of the process referred to later in this specification, to admit hydrocarbon gas to thetop of the retort. Additional branch pipes 27 with their corresponding valves 29 are also illustrated in the drawings. These merely serve as entrance ports for auxiliary reactants or diluents if desired. The preferred operation of the apparatus as follows: i

The checkerwork is first heated byapplying a heating blast through the burner pipe 17. During this heating blast the valves 25, 28, 29, 35, 36 and 37 are all closed to shut off the retort from thegas admission supplies and from the carboncollecting portion of the apparatus. The valves 18a and 19a in the pipes 18 and 19 are open .to

admit a combustible mixture. of gas and air through the burner pipe 1'7. The valve 22 is open wide to allow the gases of combustion to pass off into the stack. The heating blast is maintained until the checkerwork is heated to the desired- The checkerwork in. the zone B an oxidizing effect to clean the checkerwork by burning off the carbon depositedthereon. The combustion of this carbon of course furnishes heatv After the checkerwork bas been heated sufilciently, the blast is shut off and the cap valve 22 is closed, the outlet valve 37 is opened, the valves 25 are opened to admit the diluent 'gas at the top of the retort, and the valves 35 are opened to admit the hydrocarbon or run gas into the mixin chamber 31. The diluent gas flowing down through the heating zone A is highly preheated to a temperature well above the decomposition temperature of the hydrocarbon gas. The volume of the hydrocarbon gas, so that the sensible heat ofcompletely into hydrogen and solid carbon parti-- cles. Part a: the carbon becomes deposited on the checkerwork, while the remainder of it; is

. 1L swept along by the efliuent gas through the outlet 2 and is recovered. v

The decomposition of the hydrocarbon gas into hydrogen and carbon particles is apparently a surface phenomenon. The decomposition .apparently takes place, ortakes place initially, at the highly heated surfaces 'of the refractory checkerwork, and the carbon particles so formed are partly lodged upon the checkerwork and are partly swept along and entrained'in the stream of gas.

In order to secure an adequate yield of carbon, the zone in which the hydrocarbon gas is decomposed should contain extensive hot contact surfaces. In the form of reto'rts illustrated, such surfaces are provided by the checkerwork. We

use the word.checkerwork as a term of general description and not of limitation, and intend to include under such term materials of any shape, whether in the form of regular brick or-not, so placed in the retort chamber as to expose extended surfaces with passages between them to permit the flow of the gas. We use the word checkerwork to distinguish such a construction on theone hand from an open chamberv in which the only surface presented is that of'the chamber walls which is so small that but little decompositions of the hydrocarbon gas would result, and on the other hand from beds of granular material in which the pieces of material and the passages between them are sosmall that the carbon would be practically all caught inthe bed of material and could not be recovered.

Other specific forms of extensive"-heated con tact surfaces may beprovided in whole or in part by a heat-resisting metal structure, although we prefer to use refractory bricks, such as silica or silicon carbide brick, in a retort like that illus- .trated, in-which the heatingblast is periodically applied through the reaction zone.

We'have found that for the best results, the

hydrocarbon gas should be'quickly and thoroughly mixed with the preheated diluent gas and then the mixture rapidly swept through the checkerwork reaction zone B. If thehydroparbon gas is carbon gas were slowly mixed with a preheated diluent gas, objectionable compounds, such as naphthalene would be formed. The hydrocarbon gas would begin to decompose. but instead of decomposing quickly and entirely into carbon and hydrogen, which occurs upon quick heating, the gas would decompose partly into oily intermediate compounds. It is therefore preferred to highly preheat the diluent gas and quickly mix it 45 slowly heated, such for example, as would occur the diluent gas were unheated or if the hydrowith the hydrocarbon gas. The-high preheating lower temperature and had'to be heated by the zoneB. The checkerwork in the zone B can r tic ll necessa1 the inert diluent gasimmediately raises the temtherefore be limited to that p ac a y w perature of the. hydrocarbon gas in the mixing chamber 31 above the decomposition point. This ber 31, the temperature of the resultant mix is well above the decomposition point of the hydrocarbon gas. The gas raised to this temperature is therefore in condition to be immediately decomposed by what is apparently .the surface contact action of the extensive hot contact surfaces in the reaction zone B. The volume of diluent gas is preferably in excess of the hydrocarbon gas, 5 the volumes of the gases being computed, of course, at the same temperature for purposes of comparison. The volume of the diluent gas is preferably at least twice that of the hydrocarbon gas. Usually the ratio of volume of diluent gas to hydrocarbon gas is about three or four toone. The volume of diluent gas may be increased above this proportion without materially altering the character of the carbon, but for motives of economy, a volume of diluent gas greater than necessary should not be used. We prefer to use a dilution ratio of not over about six volumes of diluent gas to one volume of hydrocarbon gas, although such ratio may be exceeded without spoiling the carbon. We have-found that if the volume of diluent gas be reduced below about twice that of the hydrocarbon gas, the carbon will grade off with the reduction in volume of the diluent gas toward the characteristics ,of the carbon made by the Brownlee and Uhlinger process in which no diluent gas is used.

The presence of the large volume of diluent gas profoundly modifies the carbon from that produced by the Brownlee and Uhlinger process, or that whichwould be produced by a process in which but a relatively small amount of diluent gas might be used. When a hydrocarbon gas, such as natural gas, is decomposed in a retort as in the Brownlee and Uhlinger'process, a carbon black' is produced which we designate herein by the term Brownlee and Uhlinger carbon black and which is of a grayish cast and which contains a larger proportion of large carbon particles than our carbon black. The same would be true if a relatively small amount of a diluent 40 gas were mixed with the hydrocarbon gas. These large carbon particles apparently persist as such when the carbon is milled into rubber or other media. The carbon particles as initially formed at the contact surfaces in the Brownlee and Uhlinger process are an environment rich in hydrocarbon and they apparently serve as deperature of the gaseous mixture in the-mixing chamber 31, which flows through the reaction zone B. This reduction in temperature depends upon the dilution ratio.

Assuming that the gases emerging from the bottom of the checkerwork zone A have a temperature of about 1400 C. and assuming a dilution ratio of one part of the hydrocarbon gas at room temperature to three parts of such diluent gas, a calculation based solely upon the cooling effect of this volume of hydrocarbon gas upon the diluent gas indicates that ,the temperature of the mixture would be in the neighborhood of 1050 C. Moreover, the reaction whereby the hydrocarbon gas is decomposed into carbon and hydrogen is endothermic, thus further tending to cool. the mixture.

At temperatures which are practically obtainable for the mixture, the rate of decomposition of the hydrocarbon gas, without the use of hot contact surfaces, would be entirely too slow for practical operation. Because of the money invested, the decomposing retorts must be worked at a fairly high capacity. Therefore,

the stream of gas must flow rapidly through any commercial gas decomposing retort. Moreover, ifthe carbon once formed remains in the heated retort too long, it tends to become coarse or graphitic in texture and gray in color. It is therefore desirable, both for economy in operation and for attaining the desired product, to speed up the decomposing reaction by the use of extensive hot contact surfaces.

These hot contact surfaces have the dual function of bringing up the mixture formed by the composition centers or nucleii which grow in preheated diluent gas and. the cold hydrocarbon size due to further decomposition of the hydrocarbon gas.

When the hydrocarbon gas is sumciently diluted as in our process, the carbon particles as initially formed upon the contact surfaces are in an environment in which the molecules of c the hydrocarbon gas are well dispersed in the diluent so that the carbon particles do not have the same opportunity to grow in size.

The extensive hot contact surfaces afforded by the checkerwork speed up the decomposition of the hydrocarbon gas and allow it to proceed rap- GO idly at a temperature practically obtainable in a retort. If an attempt were made to decompose the hydrocarbon gas by mixing it witha highly (preheated diluent gas without extensive hot con--v tact surfaces, but little decomposition of the hydrocarbon gas would result within a practicable time. Moreover, a temperature which would be destructiveof the ordinary refractories would be required to get any substantial decomposition at all without the contact surface action.

For eflicient and rapid decomposition of a hydrocarbon gas into a carbon black having the characteristics of our carbon black, it seems to be necessary that extensive hotcontact surfaces be provided to accelerate the decomposition of gas to the proper operating temperature and supplying heat to maintain the endothermic decomposing reaction, and of exerting the so-called catalytic or'surface action in speeding up the decomposing reaction at the operating tempera ture. I

The diluent gas preferably consists principally of inert gas and by inert gas, we mean a gas which will not chemically combine with the hydrocarbon gas or the carbon particles entrained in the'gas to any substantial extent, as by combustion. The recirculated efiiuent gas resulting from the process, and which consists principally of hydrogen, is preferably used as the diluentga's, since it is inert and is readily available as a by-product. Moreover, the efiluent gas as it leaves the retort is not entirely decomposed, and while it. consists principally of hydrogen, it usually contains a small amount of undecomposed hydrocarbon gas. When this gas is again recirculated as a diluent gas, the residual undecomposed hydrocarbon gas again goes through the retort andis further decomposed, thus giving the maximum recovery from the original hydrocarbon gas. Also, when the excess hydrogen is taken off, as through the branch discharge pipe 12, and utilized as hydrogen, it is advan-' the excess hydrogen taken of! through the discharge pipe 12 will not be contaminated by other gases. However, other gases may be employed as the diluent gas, preferably inert gases, such as nitrogen.

While in the original dilution process, as developed by us and described as the preferred practice in this application, the cooled hydrogencontaining diluent gas is piped back and reheated by passing it through highly heated checkerwork, the diluent gas might be otherwise heated before it is mixed with the hydrocarbonigas to be decomposed. I

The hydrocarbon gas to be decomposed ispreferablynatural gas which can be secured cheaply, particularly from wells which are distant from industrial centers. The natural gas consists principally of methane. However, other hydrocarbon gases may be used, such for example, as

still gas from the petroleum-refining industry,

casing head gas, a gasifled or vaporized oil, gases made from coal, etc.

As above described, the usual preferred procedure is to highly preheat the diluent gas and then quickly and thoroughly mix it with a. hydrocarbon gas and pass the resultant mixture rapidly through a hot checkerwork reaction zone. This results in the carbon having the characteristics hereafter more fully described and which we designate herein asfour new carbon black.

The process may be modified and still a carbon produced having the desirable characteristics, by mixing the diluent gas and hydrocarbon gas before heating. For example, instead of admitting the hydrocarbon gas through the pipes 32, the hydrocarbon gas may be admitted through the branch pipes 26 into the diluent gas which 'passes into the top of the retort; The current of cold mixed gas then passes down through the entire column of checkerwork in the retort. This procedure gives, of course, the large volume of diluent gas and maintains the black color and lesser weight per unit volume of,the carbon. There is, however, a greater tendency for a low ered production of carbon, since in order to heat .J. Ind. & Eng. Chem. .(Analytical Edition) 4,

pp. 157-162.) v

2. It has approximately the same apparent gravity or bulking value, namely 12 to 25 pounds per cubic foot. Expressed in slightly different terms, the apparent density of'our new carbon black in grams per c. c. is approximately 0.37, as compared to 0.65 for the Brownlee and Uhlinger carbon black, 026' for a rubber black prepared by the channel process, 0.11 for a pigment black prepared by the channel process, and 0.12 for the carbon black prepared according to the process of Goodwin U. S. Patent 1,758,151. Apparent density is determined by filling a container with the carbon black, tappingthe container soas to fill it as completely as possible, weighing the thus filled container and then comparing the weight of this volume of carbon with the weight of an equal volume 'of water.

3. It has the same specific gravity in media, such as oils and rubber, namely, 1.75 to 1.79.

when incorporated into rubber in suitable proportions, the ultimate tensile values of the cured compounded stock are practically the same as those of a rubber stock containing an equal proportion by weight of common commercial rubber bon. Under certain conditions, a slight tendency toward a grayish black as distinguished from a jet black may be noticed. In degree of-blackness, its color is much closer to the channel blacks than it is to the Brownlee and Uhlinger car-- bon. In order'to remove as much as possible the human equation from the determination of the tinting strength of our carbon black, a standard up the gases, they must be passed through a sample of the same has been compared with a greater amount of checkerwork than the mixture is passed through when the hydrocarbon gas is mixed with the preheated diluent gas, with the consequently greater chance of the carbon becoming encrusted upon the checkerworl: and thus lost.

\ Having described the process of producing our new carbon black, we will now describe itsoharacteristics with particular reference to those of the usual commercial carbon blacks, such as the channel blacks, on the one hand, and tothose of the Brownlee and Uhlinger carbon black on the other hand. 1

Our new carbon black resembles common commercial carbon black in the following particulars: 1. It is a very'finely divided fluify black powder consisting of particles or aggregates, or both, a large percentage of which are submicroscopical in size. The a'verageparticle-size appears to be somewhat larger than that "of common commercial carbon black but much smaller than that of the Brownlee and-Uhlinger carbon black, being approximately 0.159;, as compared to 1.12;; for the Brownlee and carbon black, 0.061; for a'rubber black prepared by the channel process, and0.025 for a pigment black prepared by the channel process. f'-(Deterinined by the procedures described by Gehman and Morris,

standard channel black using a Keuflel and Esser color analyzer. This spectrophotometer was used to determine the brightness of various tints of each in order to eliminate inaccuracies due to difference in undertone. The spectrophotome eter separates the light reflected from the surface of the sample being tested into a visible spectrum and enables the observer to determine the brightness of the light emanating from the surface being tested relative to that from a standard white at various different" wave lengths throughout the visible spectrum. In using this color analyzer, the standard with which comparisons for brightness are made is the surface of a block of pure magnesii iin carbonate; and the technique employed is that recommended by Keuffel and Esser. a

A-master paste was made up of our new carbon black and another master paste of a standard commercial rubber black produced by the channel process, these pastes being made from the specifled carbon, z'mc oxide (XX grade) and pale ,yellow raw linseed oil. Iri'each case; onepart by weight of carbon, five parts zinc oxide and willcient weighed oil were usedtomake a paste of the desired consistency. the whole being thoroughly were toned down by the addition of zinc oxide and more oil to obtain tints of the desired concentrations (ranging from the pure carbon to the pure zinc oxide).

For example, it was desired to make a paste containing three parts by weight of our new carbon black per 100 parts of zinc oxide. A small portion of the master paste of our new carbon black (containing 12.79% carbon) was found to weigh .2997 grams. This contained .03828 grams of carbon and five times as much zinc oxide. 1.0846 grams of zinc oxide were added, together with .21 grams of linseed oil, this being the amount of oil necessary to give a paste of the proper consistencey to disperse the pigment.

The master pastes were pressed out between carefully selected glass microscope slides, and spectrophotometric determinations made of the percentage brightness relative to standard magnesium carbonate at various wave lengths by means of the color analyzer. The data were reduced to terms of percentage brightness relative to standard noon sunlight according to the method outlined by Keuffel and Esser.

The concentration of channel black necessary to produce a brightness equal to that of a .paste containing 2.5 parts by weight of our new carbon black per 100 parts of zinc oxide was obtained with the aid of agraph plotted with the logarithm of the brightness against the-logarithm of the concentrationof the carbon in parts per hundred parts of zinc oxide plus carbon.

From this the tinting strength of our new carbon black relative to the channel black at this particular concentration was calculated as the number of parts by weight of the channel black per 100 parts of our new carbonblack necessary to produceequal brightness when added to equal amounts of zinc oxide.

In testing the product ofthe checkerwork apparatus disclosed herein, it has been found that from time to time the tinting strength of the carbon black varies. Tinting strength, as the term is used herein, and as ordinarily used in this art, is defined as follows, in accordance with the definition approved by the American Society for Testing Materials: The power of coloring a given quantity of paintor pigment selected as a medium standard for estimating such power. Tests were made from time to time as above mentioned; and, in general, the method outlined in the Bureau of Mines Bulletin No. 192, 1922, Carbon Black-Its Manufacture; Properties, and Uses, by R. 0. Neal and G. St. J. Perrott, on page 62, was followed, zinc oxide-linseed oil paint being tinted with the carbon black being tested. In

' testing, the black which has come from the parts of zinc oxide. In making the test, the

carbon blackbeing tested is mixed with standard zinc oxide and refined linseed oil. The concentration of the carbon black being varied in successive pastes until, when spread in a thin film on amircroscope slide beside a film of our standrelative to channel black having been determined ard carbon black paste, a match is obtained. The tinting strength of our standard carbon black,

k with the aid of the color analyzer, the variation in thtintin strength of the product of the checker-work apparatus relative to our standard ,carbon black determined by means of these color slides gives an accurate index of the variation in the tinting strength of our new carbon black from time to time relative to channel black. These tests show that from certain checkerwork apparatus the variation in tinting strength, when samples are compared with apaste having a concentration of 2.5 parts by weight of our standard carbon black per parts of zinc oxide, is from 42 to 48% relative to a standard commercial rubber black produced by the channel process. The range may extend from as low as 40% to as high as 50% for this particular concentration. It has been found that the tinting strength of the Brownlee and Uhlinger carbon black, determined similarly, ranges from 13 to 15% relative to a standard rubber black produced by the channel.

process and may range from as low as 12 to 16% for this particular concentration of carbon black. Expressed in terms of the Brownlee and Uhlinger carbon black as a standard, by a recalculation of the above figures by simple proportion, the tinting strength of our new carbon black may be expressed as 250% to 400% that of the Brownlee and Uhlinger carbon black.

Our new carbon black differs from common commercial carbon black in the following particulars:

1. It mills into rubber much more quickly and easily. r

2. Uncured rubber stocks-i containing our new carbon black in 20 volume lqadings are not nearly sostiff as those-containing an equal weight of common commercial rubber black produced by the channel process, having a modulus at 500% elongation of approximately 2000, as compared to approximately 1800 for the Brownlee and Uhlinger carbon black, 3000 for common commercial rubber blacks produced by the channel process, and'3900 for the carbon black of the Goodwin patent referred to above, when comparedat optimum cures, in a formula containing 100 parts smoked sheet rubber, '40 parts carbon, 5 parts zinc oxide, 3.5 parts sulphur and 1.25parts diphenyl guanidine.

3. Cured rubber stocks containing our new carbon black have a much greater elongation before rupture than those containing an equal proportion by weight of common commercial rubber blacks produced by the channel process.

4. Our new carbon black has a much lower oil absorption than common commercial carbon black, the oil absorption number being usually less than 100, and generally being between 35 and 50 c. c. of refined linseed oil per 100 grams of carbon, this being the minimum. amount of oil which will give' a coherent mass without much staining of the glass plate when the mixture is well kneaded with a stiff spatula. A satisfactory grade of our carbon black as commercially produced will have an oil absorption number of approximately 40 or slightly lower.

5. Our new carbon black slightly accelerates the rate of cure of rubber compounds, whereas most common commercial carbon blacks do not accelerate the cure and usually retard it.

6. Much larger proportions of our new carbon black may be milled into rubber advantageously than is the case with common commercial carbon blacks. The maximum reinforcement of rubber by common commercial carbon black is reached with proportions of approximately twenty volumes of carbon black to one hundred volumes of rubber.

(See William B. .Wiegan'd's The Resilientv Energy Criterion; Industrial and Engineering Chemistry, vol. 1'7, p. 623, 1925). The maximum reinforcement is reached with our new carbon black at about thirty volumes of our carbon black to one hundred volumes of rubber. Furthermore, as the proportions of common commercial carbon black are increased over twenty volumes per one hundred volumes of rubber, the desirable properties of the rubber stock fall off very. rapidly and the stock becomes too stiff to be useful. On the other hand, as much as forty volumes of our new carbon black may be added to one hundred volumes of rubber without any serious deterioration of the quality. Useful stocks have been made with as much as forty volumes of our new carbon black and thirty-five volumes of other constituents, a total of seventy-five volumes, to one hundred volumes of rubber, a result quite impossible in the case of common commercial carbon black.

The maximum amount of carbon which may be milled into a rubber stock aifords still another method of distinguishing our new carbon black from other forms of carbon black. In determining the maximum loading volume values of carbons the usual procedure is to take 400 grams of clean smoked sheets and break them down by milling for 5 minutes at a rolling temperature of 140-150" F. on a. 12" mill run by a 7.5 H. P. motor. The carbon under investigation is then added as rapidly as the rubber will take it and until the rubber begins to break up. Under these conditions approximately 150 volumes of our new carbon black may be milled into 100 volumes of rubber, as compared to 59.3 volumes of a rubber black produced by the channel process, 62.9 of the carbon black of the Goodwin patent referred to above and approximately L85 of the Brownlee and Uhlinger carbon black.

- Our new carbon black resembles the Brownlee and Uhlinger carbon as follows:

1. Our new carbon .black has about the same a low oil absorption as the Brownlee and Uhlinger carbon black, namely, an oil absorption number usually below 100 and generally about 35 or 50, and therefore, it increases the viscosity of an oil vehicle approximately the same amount as the Brownlee and Uhlinger carbon black. As a gen--' eral rule, its oil absorption number will be slightly higher, say 5 to points, than that of corresponding grades of the Brownlee and Uhlinger carbon black.

fill

2, On a volume loading basis, the modulus at 500% elongation of our new carbon blacl; ,is approximatelyequal to that of an equal yolume loading of the B rownlee and Uhlinger carbon black, and approximately two-thirds that of an equal volume loading of a common commercial rubber black produced by the channel process,

- when compared at optimum cures.

' black in color, but is decidedly blacker than the Brownlee and Uhlinger carbon black which is a. dark gray (for a more detailed comparison, reference may be had'to the data given above).

- 2. Our new carbon black weighs from 12 to pounds per cubic foot, whereas the Brownlee and Uhlinger carbon black weighs from 25 to pounds per cubic foot.

3. Our new carbon black imparts an ultimate tensile strength to cured rubber compounds 5- equivalent to that of similar compounds containing an equal weight of the best varieties of common commercial rubber blacks produced by thechannel process, whereas similar compounds containing-an equal weight of the Brownlee and Uhlinger carbon have a lower ultimate tensile strength, when compared at optimum cures.

4. Rubber compounds containing our new carbon black have a much greater elongation at the point of rupture, a muchhiglier resilient energy at the point of rupture, (or proof resilience as termed by Wiegand supra), and a much greater resistance to tear, than similar compounds containing an equal weight ofthe Brownleeand Uhlinger carbon black, when compared at optimum cures.

5. Much higher proportions of our new carbon black may be advantageously used in rubber compounds than can be employed in the case of the Brownlee and Uhlinger carbon.

The stifiness of rubber as the term is used above and as ordinarily used in this art is measured in terms of the load at a given elongation of a test piece. This is commonly measured by determining the load in pounds per square inch of rubber, calculated on the original-cross section of the test piece, that is necessary to stretch the test piece to six times its original length.

The oil absorption is usually measured by the well-known Gardner test in which a refined linseed oil is mixed with the carbon black in such proportions that the mass may be rolled into a ball and begin to smear a clean smooth glass or our new carbon black is particularly valuable for compounding in rubber stocks.

It may be incorporated in the usual way in P which the carbon blacks are incorporated in rubber, namely, by milling the carbon black into the raw rubber. The rubber thus compounded is cured or vulcanized in the usual way. The rubber compositions having our new carbon black incorporated or compounded therein have certain characteristics distinguishing them from rubber compositions compounded with common vcommercial carbon black or with the Brownlee and Uhlinger carbon black. In referring to the characteristics of rubber compositions containing our new carbon black or rubber compounded with our new carbon black, we intend to refer to- Brownleeand Uhlinger carbon black. Rubber compositions containing our new carbon black have a greater elongation at point of rupture than rubber compositions containing the same weight of either common commercial carbon black or the Brownlee and Uhlinger carbon black. Rubber compositions containing our new carbon black have higher resilient energy at rupture and a greater resistance to tear than rubber compounded with an equal weight of the Brownlee and Uhlinger carbon black. A-rubber composition may contain a much larger proportion of our'new carbon black without losing its desirable qualities than is possible with either the common commercial carbon blacks or the Brownlee and Uhlinger carbon black.

The Brownlee and Uhlinger carbon black known as iThermax has been described in detail herein and is more completely described in the. Brownlee and Uhlinger patents herein referred to. This carbon black, which has been utilized as a standard of comparison for the description of our new carbon black P-33, is referred min the appended claims as the herein described thermal decomposition carbon black of the type prepared in the absence of substantial concentrations of diluent gases. v

While we have described in detail the preferred embodiments of our invention and the preferred process of operation, it is to be understood that the invention is not so limited, but may be otherwise embodied and practicedwithin the scope of the following claims.

We claim:

1. As a new article of manufacture, a carbon black, identified by the following combination of physical characteristics; (1), having a weight when uncompressed between 12 to 25 pounds per cubic foot; (2), an' oil absorption number of from 35 to 50 c. c. of refined linseed oil per 100 grams of carbon by the Gardner method; and.

(3), the property of imparting to rubber when incorporated therewith as a reinforcing agent an ultimate tensile strength of the order of 5000 and a modulus of the order of 2000 at 500% elongation, in a formula consisting of 100 parts smoked sheet rubber, 40 parts carbon, parts zinc oxide, 3.5 parts sulphur and 1.25 parts diphenyl guanidine.

' 2. As a new article of manufacture, a carbon black, identified by the following combination of physical characteristics; (1.) having a weight when uncompressed between 12 to 25 pounds per cubic foot; (2), an oil absorption number of from 35 to 50 c. c. of refined linseed oil per 100 grams carbon by the Gardner method; and (3), having the characteristic .of imparting to rubber, when compounded therewith as a reinforcing agent, a modulus of the order of ,2000 at 500% elongation at optimum cure in a formula consisting of 1000 parts smoked sheet rubber, 40 parts carwhen, 5 parts zinc oxide, 3.5 parts sulphur and 1.25

parts diphenyl guanidine. g

3. As a new article of manufacture, a. carbon black, identified by the following combination of physical characteristics; 1) having a weight when uncompressed between 12 to 25 pounds perblack, identified by the following combination of physical characteristics; (1), an oil absorption number 'of 35 to 50 c. c. of refined linseed oil per 100 grams of carbon by the Gardner 75.

method; (2), an apparent density, of the order of 0.37; (3), having a maximum volume loading value in rubber when compounded therewith as a reinforcing agent of in excess of 100, but not substantially in excess of 150; and (4) the property of imparting to rubber when incorporated therewith as a. reinforcing agent an ultimate tensile strength of the order of 5000 and a modulus of the order of 2000 at 500% elongation, in a formula consisting of 100 parts smoked sheet rubber, 40 parts carbon, 5 parts zinc oxide, 3.5 parts sulphur and 1.25 parts diphenyl guanidine.

5. As a new article of manufacture, a carbon black, identified by the following combination of physical characteristics; .(1), an oil absorption number of from 35 to 50 c. c. of refined linseed oil per 100' grams ,ofcarbon by the Gardner method; (2), an apparent density of the order of 0.37;-and (3) having a maximum volume loading value in rubber when compounded therewith as a reinforcing agent of in excess of 100, but not substantially in excess of 150.

6. As a new article of manufacture, a carbon black, identified by the following combination of physical characteristics; (1), an oil absorption number of from 35 to 50 c. c. of refined linseed oil per 100 grams of carbon by the Gardner method; (2), a tinting strength at a concentration of 2.5 parts by weight of carbon black per 100 parts of zinc oxide of from 250% to 400%, using as a standard of comparison the herein described Brownlee and Uhlinger thermal decomposition carbon black; and (3) having a maximum loading volume value in rubber when compounded therewith as a reinforcing agent of in excess of 100, but not substantiallyin excess of 150.

7. As a new article of manufacture, a carbon black, identified by the following combination of physical characteristics; (1), having a tinting strength at a concentration of 2.5 parts by weight of carbon black per100 parts of zinc oxide of from 250% to 400%, using as a standard of comparison the herein described Brownlee and Uhlinger thermal decomposition carbon black; (2) an oil absorption number of from 35 to 50 c. c. of refined linseed ofl per 100 grams of carbon by the Gardner method; and (3), having a weight when uncompressed between 12 to 25 pounds per cubic foot.

"8. As a new article of manufacture, a carbon black, identified by the following combination of physical characteristics; (1), having a tinting strength at a concentration of 2.5 parts by weight of carbon black per 100 parts of zinc oxide of from 250% to 400%, using as a standard of comparison the herein described Brownlee and Uhlinger thermal decomposition carbon black; and (2), an oil absorption number of from 35 to. 50 c. c. of refined linseed oil per 100 grams of carbon by the Gardner method.

9. As a new article of manufacture, a carbon black, identified by the'following combination of physical characteristics; (1), having a tinting strength at a-concentration of 2.5 parts by weight of carbon black per 100 parts of zinc oxide of from 250% to 400%, using asa standard of comparison the herein described Brow'nlee and Uhlinger thermal decomposition carbon black; (2) an oil absorption number of from 35 to 50 c. c. of refined linseed oil'per 100 grams of carbon 4 by the Gardner method; (3) an apparent density loading volume value in rubber when compounded therewith as a reinforcing agent of in excess of 100, but not substantially in excess of and (5), theproperty of imparting to rubber when incorporated therewith as a reinforcing agent an ultimate tensile strength of the order'of 5000 and a modulus of the' order of 2000 at 500% elongation, in a formula consisting of 100 parts smoked sheet rubber, 40 parts carbon, 5 parts zinc oxide, 3.5- parts sulphur and 1.25 parts diphenyl uanidine.

10. As a new article of manufacture, a carbon black, identified by the following combination of physical characteristics; (1), having a tinting strength at a concentration of 2.5 parts'by weight of carbon black per 100 parts of zinc oxide of from 250% to 400%, using as a standard of comparison the herein described Brownlee and Uhlinger thermal decomposition carbon black; (2) an oil absorption number of from 35 to 50 c. c. of refined linseed oil per 100 grams of carbon by the Gardner method; and (3), an apparent density of the order of 0.37.

11. As a new article of manufacture, a'carbon black, identified by the following combination of physical characteristics; (1) an apparent density of the order of 0.37; and (2) having a maximum loading value in rubber when compounded therev with as a reinforcing agent of in excess'of 100,

but not substantially in excess of 150.

ELLWOOD B. SPEAR. ROBERT L. MOORE. 

